@sLaNGjI's: Thank you very much for your kind reply. I actually was already using manual with the Minify. I agree, it is better.
Started getting numerous 500 errors on my website tonight. My ISP host looked into it and told me "On further checking, I could see that there were large number of cache files under the plugin w3tc. It was the processing of these files that delayed the execution of the PHP scripts."
She "renamed the cache files and this has significantly reduced the server load."
I do understand that the changes made to this version of the plugin were very minor. It could all be a coincidence. But reporting here in case it's helpful to someone.
In the meantime, I've disabled minify in the settings.